Speaker
Description
Strong gravitational lensing by galaxy clusters is a powerful tool to probe various properties of the Universe. It enables precise reconstructions of cluster mass distributions, detailed studies of high-redshift galaxies through lensing magnification, and measurements of cosmological parameters such as the Hubble constant, H0, using time-variable strongly lensed sources such as SN Refsdal in MACS J1149.5+2223. All of these applications critically rely on accurate cluster mass models, which currently constitute the dominant source of uncertainty in time-delay cosmography. While extended-image modeling has become standard for galaxy-scale lenses, cluster-scale mass models are normally constrained using the point-like positions of tens to hundreds of multiple images. In this talk, I present the first cluster-scale extended-image mass model of MACS J1149.5+2223, constructed using deep, high-resolution HST imaging combined with VLT/MUSE spectroscopy. The dramatic increase in observational constraints yields a two-order-of-magnitude reduction in statistical uncertainties, demoting them from the dominant error source to a sub-dominant contribution in the overall error budget. This marks a critical step toward a new generation of high-precision cluster mass models. I will discuss the impact of this enhanced mass model on time-delay cosmography and present the most precise measurement of H0 obtained from this cluster to date. I will then introduce the latest state-of-the-art mass model of the Sunburst arc, lensed by the galaxy cluster PSZ1 G311.65−18.48. This model is constrained by 54 multiple images corresponding to 14 distinct star-forming knots within a single lensed galaxy, as well as additional multiple-image systems at different redshifts securely identified through deep VLT/MUSE observations and HST/JWST imaging. First attempts at extended-image modeling of the Sunburst arc will also be presented, highlighting its exceptional suitability for such analyses and its potential to reveal detailed morphology, including extremely massive stars (>100 M_sun) at z=2.37. If time permits, I will briefly present the modeling challenge of the galaxy cluster MACS J0138.0−2155, which lenses the supernova siblings Requiem and Encore, and discuss the resulting H0 value obtained using state-of-the-art point-like mass models.